I LOVE the feel of the full-size M&P.... Amazed that a slightly short grip changes it for me so much.

Agreed. The compact M&P does have a totally different feel versus the full size. When I went shopping for my Glock 26, I found the M&P compact which to me felt way better in my hand. I took home the M&P compact.

However, I think of the two you're asking about, the SR9c would be an easier carry due to it's overall slimmer feel. I recently had a SR9 but sold it to fund my M&P full size since I wanted to build on the M&P platform. It was a great feeling pistol in the hand.